A GPS (Global Positioning System) is conventionally available for a broad location-based service, which is provided to a portable device or the like such as a high-performance portable phone, namely so-called a smartphone. It is known that a GPS is out of service indoors or underground, however.
As a known method of identifying the position of a portable device indoors or underground where a GPS comes to be out of service, there is a self-contained navigation of obtaining a traveling trajectory of the portable device from a measured quantity of a distance sensor or an orientation sensor installed in the portable device and calculating a current position by adding the traveling trajectory to a start point. Patent Literature 1 proposes a technology of using a geomagnetic sensor to detect an orientation based on geomagnetism as an orientation sensor in self-contained navigation.